SAN FRANCISCO — Unless the Mets can find another major league hitter or two for their largely Quadruple-A lineup, they will remain prone to streaks like these.

On Sunday, they needed a hit of any kind from Chris Young with the tying run at third base in the eighth inning. What the Mets received — a routine fly to left field — was almost predictable.
The Mets left their hearts, and assorted other body parts, in San Francisco with a 6-4 loss to the Giants that extended their losing streak to six games.

This didn’t have the tragedy feel of a night earlier, when the Mets flushed a one-run lead in the ninth inning and watched the Giants celebrate a walk-off victory on Michael Morse’s RBI single, but it stung nonetheless.

“We need to do a better job of routinely getting runners in scoring position,” said David Wright, who struck out as a pinch hitter in the seventh inning. “It’s magnified when you only have a couple of chances in a game and you don’t come through in those chances.”

The Mets (28-35) scored four runs or fewer in each of their six losses to the Cubs and Giants to complete the road trip. The three-game sweep of the Mets at AT&T Park was the Giants’ first since 2002.

In five of their six straight losses, the Mets held a lead at some point — including Sunday.

“We had the lead in a lot of them — almost every night,” manager Terry Collins said. “What we’ve got to do is do a better job of trying to hold it and certainly add on. You saw what they did, they kept adding on a run when they needed it, got big hits when they needed it, and we haven’t been able to do that.”

After Young failed to produce in the eighth against Jean Machi, the Giants got an insurance run in the bottom of the inning. Brandon Crawford doubled against Scott Rice and Brandon Hicks followed with an RBI single against Vic Black to put the Mets in a 6-4 hole that seemed insurmountable.

The Mets head home for six games against the Brewers and Padres beginning Tuesday. For most teams, the return home would be welcomed, but considering the Mets are 13-17 at Citi Field this season, it might be difficult to tell.

In the shortest start of his major league career, Zack Wheeler lasted only 3 ²/₃ innings. He allowed four earned runs on six hits with six strikeouts and two walks. The right-hander was replaced by Josh Edgin with two runners on in the fourth and the Mets trailing 4-2.

“This is definitely not the start that the team needed out of me,” Wheeler said. “I needed to go deeper into the game and not let up any of the runs that I let up. I really didn’t have fastball command, everything else was working for me.”

It was a step backward for Wheeler, who had dominated in consecutive starts against the Phillies and Cubs. In the latter performance he pitched a two-hit shutout over 6 ²/₃ innings, but received a no-decision.

Carlos Torres had a second straight lackluster appearance for the Mets. The right-hander surrendered an RBI single to Gregor Blanco in the seventh that gave the Giants a 5-3 lead. Two nights earlier, he had allowed a two-run homer to Buster Posey in the eighth inning that put the Giants ahead.

Curtis Granderson’s second homer of the game, a solo blast into McCovey Cove in the sixth, pulled the Mets to within 4-3 against Tim Lincecum.

Granderson also hit a two-run homer in the first to stake the Mets to a 2-0 lead. The multiple-homer game was his first in a Mets uniform and gave him eight homers and 30 RBIs this season.

After 20 straight days with a game, the Mets gladly will take Monday off.